1. Field of the Invention
This invention relates to an anisotropic road surface and a method of preparation thereof. More particularly, the invention relates to a road surface which is anisotropic in behavior (i.e., exhibiting different properties when tested along axes in different directions), as compared with road surfaces which are isotropic in behavior (i.e., having the same properties in all directions).
2. Description of the Prior Art
Prior to the present invention, various processes have been proposed for the construction of road surface courses. One of the most recent proposals consists of prefabricating the surface by mixing hot asphalt with an inert filling material, the particles of which are between 0.1 mm and 14 mm, for example, and then spreading the hot mixture thus obtained on a suitably prepared road surface. Such process has been found to lead to the production of a surface course having, to a sufficient degree, isotropic properties, i.e., properties which are the same whether measured in the direction of the thickness of the surface course or along an axis parallel to the surface of the course.
U.S. Pat. Nos. 1,834,835 and 1,918,155 show isotropic road surface preparations. A detailed analysis of the desirable properties for such a surface course and the stresses to which the surface course will be subjected, leads to the conclusion that it is desirable to have a surface course presenting anisotropic mechanical properties, i.e., mechanical resistance which is as large as possible in the direction of the thickness of the surface course, and a certain deformability in all perpendicular directions.